in BUCCAL CAVITY 149 



It is, as a matter of fact, quite continuous with the ectoderm, 



to. 



Fig. 82. — Sagittal section through head region of a Protopterus larva (Stage 33). 



b.c, buccal cavity; b.t, anterior boundary of tongue; N, notochord ; pin, pineal body; par, 

 paraphysis ; Pit, pituitary body ; Th, thyroid rudiment ; (.a, tectum opticum. The position of dental 

 rudiments is indicated by the two upward projections of the dorsal wall of the buccal cavity. 



but examination of carefully prepared celloidin sections (Fig. 83) 

 shows that at its inner end the epithelium passes by imperceptible 



Fig. 83. — Sagittal sections through the region of the buccal cavity of (A) Lepidosiren, 

 stage 30, and (B) Amblystoma, 7 '5 mm. in length. 



&.e, buccal epithelium ; eet, ectoderm ; y, solid mass of yolk-cells in position of buccal cavity. 



gradations into the ordinary yolky endoderm, with no trace of the 

 sharply defined edge which it would possess were it a layer of 



